1. Field of the Invention
This invention relates generally to a radio controlled, battery-operated model toy, and more specifically to a radio controlled, battery operated model toy in which a battery device for supplying energy to an electric motor is used to supply power to both a radio control receiver and a steering servo mechanism so as to make full use of the reserve power of the battery device.
2. Description of the Prior Art
In general, radio controlled model airplanes, radio controlled model ships and other radio controlled model toys have a separate battery device as a power supply for a radio control receiver and a steering servo-mechanism in addition to a battery device for supplying electric power to an electric motor which drives a propeller.
In recent years, nickel-cadmium batteries have been increasingly used as an energy source for electric motors for the following reasons; nickel-cadmium batteries are small in size, light in weight, have an extremely small internal resistance, and provides a large discharge power relative to its weight. In addition, the terminal voltage drop of these Ni-Cd batteries is very small compared with conventional manganese batteries despite of large discharge current, resulting in long effective discharging time.
In model toys, an extremely low supply voltage is inconvenient in practical use since low supply voltage requires large current to obtain the required power and tends to drop because of the resistance of lead wires. Therefore, several Ni-Cd batteries with the terminal voltage of approx. 1.2 V are usually connected in series. An individual Ni-Cd battery can be recharged even after it has been discharged to nearly zero voltage. However, when used in series connection, some batteries may often be depleted faster than others. In such a case, the polarity of the depleted batteries is apparently reversed by the current supplied by other batteries, leading to reverse charging and eventually permanent deterioration of batteries. For this reason, special consideration is required to prevent excessive discharge in a battery device comprising series-connected batteries. For example, a device is known which automatically disconnects the battery device from the electric motor when an average voltage per battery in the battery device drops to approximately 0.7 V.
In the case of such a battery device, there is a possibility of reverse charging when supplying an electric motor requiring a discharge current of, for example, 10 A, as mentioned above, but there is a sufficient reserve power when supplying a load of for example, 300 mA. Therefore, it is desired that a battery device is used not only as a power supply for the electric motor but also as a power supply for the radio control receiver and the steering servo-mechanism to use the above mentioned reserve power in driving the receiver and the servo-mechanism. Needless to say, it is required that batteries comprising a battery device be protected against reverse charging.
When a battery device is used as a common power supply for several purposes, the following points must be satisfied.
(1) Even when gradual voltage fluctuations occur in a battery device, these fluctuations should be regulated to such an extent that the radio control system can ignore it. PA1 (2) When a pulse-shaped noise of relatively short period is generated in the battery device, such a noise should be almost perfectly filtered to an extent that the radio control system cannot pick it up. PA1 (3) In a model toy such as a model ship which may drift away offshore beyond recovery because of depletion of power, power to the electric motor cannot be interrupted, unlike a model airplane, even when the terminal voltage of the battery device drops. It is necessary, therefore, to supply the electric motor with a sufficient level of electric current to prevent batteries comprising the battery device from reverse charging and yet to enable the model toy to be recovered, for example, a current of approx. 1 A.